Editing revision 5 of ReactionStoichiometry

ApchemWiki | RecentChanges | Preferences

Editing old revision 5. Saving this page will replace the latest revision with this text.

1. Write the balanced equation (reaction).

2. Convert the known information (e.g. mass) of the reactant to moles. 
 A. If you need help on determining the apporpriate equation, look at the graphic organizer.
 B.Will modify this step when we get to the Limiting Reactant problems.

3. Use the balance equation to set-up the right "molar ratio" to go from the known substance to the unknown substance.

4. Convert from the moles of the unknown susbtandce to tue unknown information (e.g., are you looking for mass, volume, # of particles)
A. Again, if you need help on determining the appropriate equation, look at the Graphical Organizer.

Example: Calculate the mass (in grams) of NH3 (ammonia) produced by the reaction of 5.4 grams of hydrogen with nitrogen. The balanced reaction equation is:

1 N2 (g) + 3 H2 (g) => 2 NH3 (g)

Step 1: Question (see balanced reaction above) gave is information

Step 2: Convert the mass of hydrogen (known substance) to moles

# moles = grams/molar mass Molar Mass of H2: (1 g)(2) = 2 g/mol

Step 3: Figure out from the balanced reaction what the Molar Ratio is between hydrogen and ammonia.

2 mole NH3 / 3 mole H2

Now use this ratio to convert from known (hydrogen) to unknown (ammonia).

(2.70 mole H2)(2 mole NH3 / 3 mole H2) = 1.80 mole NH3

Step 4: Convert from unkown (ammonia) moles to unknown information (mass).

#mole = grams/molar mass Molar Mass of NH3: (14 g)(1) + (1 g)(3) = 17 g/mol

1.80 mole NH3 = X / 17 g/mol NH3

X = (1.80 mole NH3)(17 g/mol NH3) = 30.60 grams NH3

X = 30.6 grams NH3

View other revisions
ApchemWiki | RecentChanges | Preferences